1929 Murchison earthquake
Encyclopedia
The 1929 Murchison earthquake occurred at 10:17 AM on 17 June. It struck the Murchison
region of South Island
, with an estimated magnitude
of 7.8, and was felt throughout New Zealand
. There were 17 casualties, mostly as a result of landslide
s triggered by the earthquake
. The rumbling sound of the earthquake was loud enough to be heard at New Plymouth
, more than 250 km away.
and the Pacific Plate
. In the South Island most of the displacement is taken up on the Alpine Fault
passing to the north onto a set of strike-slip faults, the Marlborough Fault System
. The sense of displacement across the plate boundary is oblique and most of the faults have a reverse component of slip. Some of the resulting deformation is accommodated within the plates themselves away from the boundary. The 1929 Murchison earthquake occurred on the White Creek Fault, located in the Buller Gorge
.
was in a sparsely populated area about 65 km north of Murchison, the shaking in the surrounding region was sufficiently intense to cause damage over a wide area. The towns of Nelson
, Greymouth
and Westport
were all affected and roads , buildings and bridges were severely damaged throughout an area estimated at 26,000 km2. The worst damage was caused by landslides triggered by the shaking, destroying several homes and killing 14 out of the 17 that died in the earthquake. Most of the buildings in the Murchison area were built of wood and were warped and moved from their piles, but many brick buildings and chimneys were damaged in Nelson, Greymouth and Westport.
s before the mainshock, accompanied by booming sounds in the mountains around Murchison. There was a large surface fault rupture visible in the Buller River
, indicating about 4.5 m of vertical movement and 2.5 m of lateral movement. The earthquake triggered many landslides and these created 38 new lakes, of which 21 still exist, including Lake Stanley. The earthquake was accompanied by unusually loud rumbling noises that were heard as far away as New Plymouth. A maximum intensity of X on the Mercalli scale has been estimated for Murchison. Most of the northern part of South Island suffered an intensity of VII or greater.
was completely cut off and received no outside help for two weeks, until a Tiger Moth
plane landed on the beach. Some of the blocked roads took months to clear.
Murchison, New Zealand
Murchison is a town in the Tasman Region of the South Island of New Zealand. It is near the western end of the "Four Rivers Plain", at the confluence of the Buller River and the Matakitaki River...
region of South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
, with an estimated magnitude
Surface wave magnitude
The surface wave magnitude scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements in Rayleigh surface waves that travel primarily along the uppermost layers of the earth...
of 7.8, and was felt throughout New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. There were 17 casualties, mostly as a result of landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s triggered by the earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
. The rumbling sound of the earthquake was loud enough to be heard at New Plymouth
New Plymouth
New Plymouth is the major city of the Taranaki Region on the west coast of the North Island of New Zealand. It is named after Plymouth, Devon, England, from where the first English settlers migrated....
, more than 250 km away.
Tectonic setting
New Zealand sits astride the boundary between the Indo-Australian PlateIndo-Australian Plate
The Indo-Australian Plate is a major tectonic plate that includes the continent of Australia and surrounding ocean, and extends northwest to include the Indian subcontinent and adjacent waters...
and the Pacific Plate
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....
. In the South Island most of the displacement is taken up on the Alpine Fault
Alpine Fault
The Alpine Fault is a geological fault, more specifically known as a right-lateral strike-slip fault, that runs almost the entire length of New Zealand's South Island. It forms a transform boundary between the Pacific Plate and the Indo-Australian Plate. Earthquakes along the fault, and the...
passing to the north onto a set of strike-slip faults, the Marlborough Fault System
Marlborough Fault System
The Marlborough Fault System is a set of four large dextral strike-slip faults and other related structures in the northern part of South Island, New Zealand, which transfer displacement between the mainly transform plate boundary of the Alpine fault and the mainly destructive boundary of the...
. The sense of displacement across the plate boundary is oblique and most of the faults have a reverse component of slip. Some of the resulting deformation is accommodated within the plates themselves away from the boundary. The 1929 Murchison earthquake occurred on the White Creek Fault, located in the Buller Gorge
Buller Gorge
The Buller Gorge is a gorge located in the northwest of the South Island of New Zealand. The Buller River flows through the deep canyon between Murchison and Westport. Land Information New Zealand lists two sections for the gorge, Upper Buller Gorge and Lower Buller Gorge. State Highway 6 runs...
.
Damage
Although the epicenterEpicenter
The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates...
was in a sparsely populated area about 65 km north of Murchison, the shaking in the surrounding region was sufficiently intense to cause damage over a wide area. The towns of Nelson
Nelson, New Zealand
Nelson is a city on the eastern shores of Tasman Bay, and is the economic and cultural centre of the Nelson-Tasman region. Established in 1841, it is the second oldest settled city in New Zealand and the oldest in the South Island....
, Greymouth
Greymouth
Greymouth is the largest town in the West Coast region in the South Island of New Zealand, and the seat of the Grey District Council. The population of the whole Grey District is , which accounts for % of the West Coast's inhabitants...
and Westport
Westport, New Zealand
-Economy:Economic activity is based around fishing, coal mining and dairy farming. Historically, gold mining was a major industry, and coal mining was much more extensive than today . However, the region still is home to New Zealand's largest opencast mining operation in Stockton...
were all affected and roads , buildings and bridges were severely damaged throughout an area estimated at 26,000 km2. The worst damage was caused by landslides triggered by the shaking, destroying several homes and killing 14 out of the 17 that died in the earthquake. Most of the buildings in the Murchison area were built of wood and were warped and moved from their piles, but many brick buildings and chimneys were damaged in Nelson, Greymouth and Westport.
Characteristics
The earthquake was preceded by several foreshockForeshock
A foreshock is an earthquake that occurs before a larger seismic event and is related to it in both time and space. The designation of an earthquake as foreshock, mainshock or aftershock is only possible after the event....
s before the mainshock, accompanied by booming sounds in the mountains around Murchison. There was a large surface fault rupture visible in the Buller River
Buller River
The Buller River is in the South Island of New Zealand. One of the country's longest rivers, it flows for 170 kilometres from Lake Rotoiti through the Buller Gorge and into the Tasman Sea near the town of Westport...
, indicating about 4.5 m of vertical movement and 2.5 m of lateral movement. The earthquake triggered many landslides and these created 38 new lakes, of which 21 still exist, including Lake Stanley. The earthquake was accompanied by unusually loud rumbling noises that were heard as far away as New Plymouth. A maximum intensity of X on the Mercalli scale has been estimated for Murchison. Most of the northern part of South Island suffered an intensity of VII or greater.
Aftermath
The landslides blocked many roads causing food supplies to run out in some areas near the epicenter. This and the risk from aftershocks and flooding from the landslides blocking rivers caused many residents to evacuate the area, mostly on foot. KarameaKaramea
Karamea is a town on the West Coast of the South Island of New Zealand.It is the northernmost settlement of any real size on the West Coast, and is located 96 kilometres north-east by road from Westport. There is no other connecting road to the town - the road north ends at the Kohaihai River some...
was completely cut off and received no outside help for two weeks, until a Tiger Moth
De Havilland Tiger Moth
The de Havilland DH 82 Tiger Moth is a 1930s biplane designed by Geoffrey de Havilland and was operated by the Royal Air Force and others as a primary trainer. The Tiger Moth remained in service with the RAF until replaced by the de Havilland Chipmunk in 1952, when many of the surplus aircraft...
plane landed on the beach. Some of the blocked roads took months to clear.